The present invention relates generally to a crank press, and more particularly to a crank press for forging and sheet metal processing.
FIG. 6 is an illustration of the basic structure of the so-called crank press. A crankshaft 1 is driven by an electric motor or the like and connected to a slider 3 by a connecting rod 2. An upper metal mold is fixed to the bottom of the slider 3, and a lower metal mold is fixed onto a bed (not shown). A work is put between the upper and lower metal molds and the slider 3 is lowered to forge or form the work into a certain shape.
Connected to the slider 3 are the piston rods 4a of a pair of balance cylinders 4, and the cylinders 4b of the balance cylinders 4 are fed with compressed air from an accumulator 5, to always exert upward force to the crankshaft 1 through the media of the slider 3 and connecting rod 2. Under the condition, the crankshaft 1 is driven to move the slider 3 up and down through the medium of the connecting rod 2.
In case of the general-purpose hot-forging crank press, the crankshaft 1 is stopped at its top dead center at the end of each cycle. To accomplish this, the conventional crank press is given a mechanism shown in FIG. 7.
Coupled to an end of the crankshaft 1 is a brake 6, which is controlled pneumatically by a brake control valve SV1 and switched between the working and nonworking states. Besides, coupled to the other end of the crankshaft 1 are a clutch 7 and a flywheel 8. The flywheel 8 is rotated by an electric motor 9 through the medium of a belt. The clutch 7 is controlled pneumatically by a clutch control valve SV2 and switched between the states of engagement and disengagement.
Referring to FIG. 6, 7 and 8, the operation of the above conventional crank press will now be described.
Now the slider 3 is at a stop at its top dead point. When a signal to initiate a pressing cycle is given, the brake control valve SV1 releases the brake 6, and then the clutch control valve SV2 engages the clutch 7. The electric motor 9 drives the crankshaft 1, and the slider 3 begins to move down. When the slider 3 reaches its bottom dead point, the clutch control valve SV2 disengages the clutch 7, and the slider 3 moves upward by the inertia force of the turning parts. While the slider 3 is moving upward, the brake control valve SV1 activates the brake 6 to stop and keep the slider 3 at its top dead point until the next pressing cycle is initiated.
By repeating the above process, the crank press operates continually, stopping the slider 3 at its top dead point at the end of every cycle.
In case of the above conventional crank press, a large capacity is required of the brake 6 in order to absorb instantaneously the large energy of the slider 3, etc. and the pulling-up force of the balance cylinders 4 and stop the slider 3 at its top dead point. Besides, a large capacity is required of the electric motor 9 in order to cause the crankshaft 1, etc. to begin to turn or move. Thus, in the conventional crank press, large energy has to be exerted and absorbed, or consumed, at the beginning and end of each pressing cycle, respectively.
In accordance with the above, the object of the present invention is to provide a crank press wherein energy is utilized effectively and, thereby, the load on the brake, the required capacity of the electric motor, and the overall noise level are reduced.